1. Field of the Invention
This invention relates, in general to electrical apparatus and, more specifically, to tap changers for power transformers.
2. Description of the Prior Art
No-load tap changers are used with power transformers to effectively change the turns ratio between the primary and secondary windings of the transformers. Conventional no-load tap changers for power transformers usually include a plurality of stationary contact structures and a movable contact assembly which may be moved into engagement with one of the stationary contacts. The stationary contacts are connected to taps on the transformer winding and the movable contact is connected to another portion of the winding or to the load associated with the transformer.
No-load tap changers for three-phase power transformers usually have separate sets of stationary and movable contacts for each winding phase. These contacts are usually connected together by a common shaft so that they may be changed simultaneously. One type of conventional arrangement used in the prior art has three sets of stationary contacts disposed in a circular arrangement around a common axis. Rotating contacts associated with these stationary contacts are positioned and adapted for rotation around the common axis to make electrical connection with one of the stationary contacts. The rotating contacts are mechanically connected to each other by a series of shafts which extend along the common axis. Thus, the tap changer has one axis of rotation and three planes which generally contain the stationary contacts of the tap changer.
Tap changing apparatus constructed according to this prior art arrangement is satisfactory but requires elaborate coupling mechanisms between each phase of the tap changer and occupies considerable space within the transformer enclosure. Therefore, it is desirable, and it is an object of this invention, to provide a three-phase no-load tap changer for power transformers which may be economically constructed and which occupies less space in the transformer enclosure than prior art no-load tap changers.